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C. Lastra Gonzalez, S. Fraser-Bell, M. Torres, R. Varma, Los Angeles Latino Eye Study Group; Optical Coherence Tomography Measured Retinal Nerve Fiber Layer Thickness Using Two Different Scan Options. Invest. Ophthalmol. Vis. Sci. 2007;48(13):176.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal Nerve Fiber Layer (RNFL) is thicker closer to the optic disc margin and thins out as ganglion cell axons approach the retinal periphery.Current Optical Cohenrence Tomography (OCT) protocols use a fixed diameter scan to measure RNFL thickness. This study examined the difference in RNFL thickness measurements between two different scan protocols, the circular 3.4mm fixed diameter scan the Proportional Circle RNFL (Prop RNFL- scan protocol that uses a proportion of the disc diameter as the scan diameter thus varying by disc size - larger discs have larger diameter scans and smaller discs have smaller diameter scans) using the STRATUS OCTTM (Carl Zeiss Meditec, inc., Dublin, CA).
Participants aged 40 years and older from the Los Angeles Latino Eye Study (LALES) - a population-based prevalence study of eye disease among Latinos - underwent a complete ophthalmologic examination a complete anterior and posterior segment evaluation by an ophthalmologist, Humphrey Visual Field testing and optic disc and fundus photography. OCT was performed on all participants using the RNFL 3.4 mm scan and the Prop RNFL protocols. Paired t-tests were used to compare the difference in RNFL thickness between the two scan patterns.
OCT scans results from 655 normal eyes were included in this evaluation. The mean (± standard deviation) overall RNFL thickness was 103 microns (± 11) using the RNFL 3.4 scan and 133 microns (±15) using the Prop RNFL protocol, the mean of absolute difference was 30 microns (p<0.0001). The mean temporal thickness was 69 microns (±11) using the RNFL 3.4 scan and 85 microns (±15) using the Prop RNFL scan. The mean superior thickness was 129 microns (±17) using the RNFL 3.4 scan and 161 microns (±22) using the Prop RNFL scan. The mean nasal thickness was 84 microns (±17) using the RNFL 3.4 scan and 118 microns (±25) using the Prop RNFL scan. The mean inferior thickness was 132 microns (±17) using the RNFL 3.4 and 168 microns (±22) using the Prop RNFL scan.
On average, the overall and quadrant specific mean RNFL thickness was consistently and significantly greater when using the Prop RNFL scan compared to the RNFL 3.4 scan. The use of the Prop RNFL scan protocol may provide a more anatomically reliable measure RNFL thickness than the RNFL 3.4 because it minimizes the effect of the interindividual variability due to different optic disc sizes. This Prop RNFL scan pattern should be further assessed to determine if the RNFL thickness measurements provide a better measure of disease related damage to the optic nerve.
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